isoimmunization: antibodies (Ab) produced against a specific RBC antigen (Ag) as a result of antigenic stimulation with RBC of another individual
maternal-fetal circulation normally separated by placental barrier, but sensitization can occur and can affect the current pregnancy, or more commonly, future pregnancies
Anti-Rh Ab produced by a sensitized Rh-negative mother can lead to fetal hemolytic anemia
Risk of isoimmunization of an Rh-negative mother with an Rh-positive ABO-compatible infant is 16%
sensitization routes
incompatible blood transfusions
previous fetal-maternal transplacental hemorrhage (e.g. ectopic pregnancy, abruption)
invasive procedures in pregnancy (e.g. prenatal diagnosis, cerclage, D&C)
any type of abortion
labour and delivery
screening with indirect Coombs test at first visit for blood group, Rh status, and antibodies
Kleihauer-Betke test used to determine extent of fetomaternal hemorrhage by estimating volume of fetal blood volume that entered maternal circulation
detailed U/S for hydrops fetalis
MCA dopplers are done to assess degree of fetal anemia or if not available bilirubin is measured by serial amniocentesis to assess the severity of hemolysis
cordocentesis for fetal Hb should be used cautiously (not first line)
exogenous Rh IgG (Rhogam® or WinRho®) binds to Rh antigens of fetal cells and prevents them from contacting maternal immune system
Rhogam® (300 μg) given to all Rh negative and antibody screen negative women in the following scenarios
routinely at 28 wk GA (provides protection for ~12 wk)
within 72 h of the birth of an Rh positive fetus
with any invasive procedure in pregnancy (CVS, amniocentesis)
in ectopic pregnancy
with miscarriage or therapeutic abortion
with an antepartum hemorrhage
a Betke-Kleihauer test or Flow cytometry can be used to determine whether more than 300 μg of RhIg is required (>30 ml fetal blood)
if Rh negative and Ab screen positive, follow mother with serial monthly Ab titres throughout pregnancy +ultrasounds± serial amniocentesis as needed (Rhogam® has no benefit)
falling biliary pigment warrants no intervention (usually indicative of either unaffected or mildly affected fetus)
intrauterine transfusion of O-negative pRBCs may be required for severely affected fetus or early delivery of the fetus for exchange transfusion
anti-Rh IgG can cross the placenta and cause fetal RBC hemolysis resulting in fetal anemia, CHF, edema, ascites
severe cases can lead to fetal hydrops (edema in at least two fetal compartments due to fetal heart failure secondary to anemia) or erythroblastosis fetalis (moderate to severe immune-mediated hemolytic anemia)